Application of Instrumented Indentation Technique to Evaluate Residual Stress and Stress Directionality

The instrumented indentation technique (IIT) is a powerful method for evaluating mechanical properties of materials such as elastic modulus, tensile strength, fracture toughness and residual stress. Especially, IIT is a promising alternative to conventional methods of residual stress measurement such as hole drilling, saw cutting, X-ray/neutron diffraction, and ultrasonic methods because of its various advantages of nondestructive specimen preparation, easy process, characterization of material properties on local scales and measurement of in-service structures. Evaluation of residual stress using IIT is based on the key concepts that the deviatoric-stress part of the residual stress affects the indentation load-depth curve and that the quantitative residual stress in a target region can be evaluated by analyzing the difference between the residual stress-induced indentation curve and residual stress-free curve. To verify the applicability of the suggested technique, indentation tests were performed on the welded zone.